Thermal phase transition for some spin-boson models

In this work we study two different spin-boson models. Such models are generalizations of the Dicke model, it means they describe systems of N identical two-level atoms coupled to a single-mode quantized bosonic field, assuming the rotating wave approximation. In the first model, we consider the wavelength of the bosonic field to be of the order of the linear dimension of the material composed of the atoms, therefore we consider the spatial sinusoidal form of the bosonic field. The second model is the Thompson model, where we consider the presence of phonons in the material composed of the atoms. We study finite temperature properties of the models using the path integral approach and functional methods. In the thermodynamic limit, N→∞, the systems exhibit phase transitions from normal to superradiant phase at some critical values of temperature and coupling constant. We find the asymptotic behavior of the partition functions and the collective spectrums of the systems in the normal and the superradiant phases. We observe that the collective spectrums have zero energy values in the superradiant phases, corresponding to the Goldstone mode associated to the continuous symmetry breaking of the models. Our analysis and results are valid in the limit of zero temperature β→∞, where the models exhibit quantum phase transitions. © 2013 Elsevier B.V. All rights reserved.

Stability and collapse of fermions in a binary dipolar boson-fermion 164Dy-161Dy mixture

We suggest a time-dependent mean-field hydrodynamic model for a binary dipolar boson-fermion mixture to study the stability and collapse of fermions in the 164Dy-161Dy mixture. The condition of stability of the dipolar mixture is illustrated in terms of phase diagrams. A collapse is induced in a disk-shaped stable binary mixture by jumping the interspecies contact interaction from repulsive to attractive by the Feshbach resonance technique. The subsequent dynamics is studied by solving the time-dependent mean-field model including three-body loss due to molecule formation in boson-fermion and boson-boson channels. Collapse and fragmentation in the fermions after subsequent explosions are illustrated. The anisotropic dipolar interaction leads to anisotropic fermionic density distribution during collapse. This study is carried out in three-dimensional space using realistic values of dipolar and contact interactions. © 2013 American Physical Society.

O modelo padrão das interações eletrofracas: aspectos fenomenológicos do setor escalar e sua extensão supersimétrica

Pós-graduação em Física - FEG

Uma abordagem de gauge para corpos deformáveis

Pós-graduação em Física - IFT

Efeito da ciclagem mecânica na deflexão de cúspides de pré-molares restaurados pela técnica direta e indireta: estudo com strain gauge

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Geração de massa em Teorias de Gauge

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Pólos no gauge do cone de luz e o método de covariantização

Pós-graduação em Física - IFT

Search for a Higgs boson decaying into a b-quark pair and produced in association with b quarks in proton-proton collisions at 7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the W-boson helicity in top-quark decays from t(t)over-bar production in lepton plus jets events in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for a Higgs boson decaying into a Z and a photon in pp collisions at root s=7 and 8 TeV

A search for a Higgs boson decaying into a Z boson and a photon is described. The analysis is performed using proton-proton collision datasets recorded by the CMS detector at the LHC. Events were collected at center-of-mass energies of 7 TeV and 8 TeV, corresponding to integrated luminosities of 5.0 fb(-1) and 19.6 fb(-1), respectively. The selected events are required to have opposite-sign electron or muon pairs. No excess above standard model predictions has been found in the 120-160 GeV mass range and the first limits on the Higgs boson production cross section times the H -> Z gamma branching fraction at the LHC have been derived. The observed at 95% confidence level limits are between about 4 and 25 times the standard model cross section times the branching fraction. For a standard model Higgs boson mass of 125 GeV the expected limit at the 95% confidence level is 10 and the observed limit is 9.5. Models predicting the Higgs boson production cross section times the H -> Z gamma branching fraction to be larger than one order of magnitude of the standard model prediction are excluded for most of the 125-157 GeV mass range. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.

Measurement of the cross section and angular correlations for associated production of a Z boson with b hadrons in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of Higgs boson production and properties in the WW decay channel with leptonic final states

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Search for the standard model Higgs boson produced in association with a W or a Z boson and decaying to bottom quarks

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Measurement of the hadronic activity in events with a Z and two jets and extraction of the cross section for the electroweak production of a Z with two jets in pp collisions at root s=7 TeV

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Measurement of the properties of a Higgs boson in the four-lepton final state

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)